Tire treads and their manufacture

ABSTRACT

Tread stock is partially cured by irradiation before assembly in the tire, so as to shorten the curing time of the tire in the mold and thereby create substantial savings. 
     Tires are retreaded by applying ribbons of tread stock over the carcass prepared in any conventional manner, and then completing the cure without the use of a mold. 
     Curing or partial curing may be effected by electron irradiation or other irradiation which changes the molecular structure of the rubber. Progressive irradiation is disclosed by which an object is repeatedly irradiated to attain a desired cure. Shielding of one or more portions of a green tire or tire element is disclosed to prevent the irradiation from curing the shielded rubber. Other methods of curing may be preferable in some operations. 
     Curing (1) a portion of the area of tread stock and (2) curing a portion of the thickness of tread stock are disclosed herein.

CROSS-REFERENCE

This application is a continuation of Ser. No. 702,623 filed July 6,1976 now U.S. Pat. No. 4,139,405 which is a continuation-in-part of Ser.No. 627,136 filed Oct. 30, 1975 which is a continuation of Ser. No.395,346 filed Sept. 7, 1973 (now U.S. Pat. No. 3,933,553) which is acontinuation of Ser. No. 321,421 filed Jan. 5, 1973 (now abandoned)which was a continuation-in-part of Ser. No. 838,512 filed July 2, 1969(now abandoned). U.S. Pat. No. 3,933,566 has matured from Ser. No.454,207 which was a continuation of Ser. No. 321,421, supra.

PRIOR ART

Marks Ser. No. 844,820 discloses semi-vulcanizing the body of a tire,roughening the surface and coating it with cement. A partiallyvulcanized tread is put in place and vulcanization is completed. Noradiation is disclosed.

Hopkinson U.S. Pat. No. 1,289,771 and Hoffman No. 1,488,343 discloseprocedures for first partially curing a tire part, and then completingthe vulcanization. No radiation is disclosed.

In Mallon U.S. Pat. No. 2,933,441 a tire is set in a mold until the bodyportion is set. The tire is removed from the mold and the tread isradiated until completely cured.

Newton U.S. Pat. No. 1,986,402 refers to curing rubber by electronirration but makes no mention of treads.

Progressive radiation of polyethylene is disclosed in Lawton U.S. Pat.No. 3,330,748.

SUMMARY OF THE INVENTION

The invention relates to radiation which changes the molecular structureof rubber and more particularly to the use of electron radiation in theproduction of new tires and the retreading of old tires, although othermeans of radiation may be employed, and for most operations other meansof curing may be used, as explained.

Electron radiation has been known for some years and in recent yearsequipment utilizing up to a million volts or more has become availablefor commercial use. The voltage employed determines the depth ofpenetration of the electron rays. For example, radiation generated by amillion volts will penetrate an item having a density of 1 to a depth of1/8 inch. By varying the voltage, the depth of the penetration may bevaried. Thus, a portion of the thickness of tires may be cured by curingto a depth of 1/8 inch or more, depending upon the rubber employed, thecompounding formula, and the voltage used. By using higher voltages andradiating both surfaces of a tire, tires of much greater thickness maybe cured. When only one surface is irradiated, beyond the depth at whichthe rubber is cured there is a partial curing which becomes less as thedistance from the rubber surface increases.

The amperage will be varied depending upon the area subjected toradiation. The new equipment provides for irradiating an area of severalsquare inches, up to for example 12 square inches or more.

By shielding one or more portions of a tire or tire element as withaluminum or other suitable material, such as steel or lead or a plastic,the area or areas to be irradiated are controlled. The material treatedand the irradiation equipment may both be stationary, or at least onemay be moved with respect to the other during the irradiation. The shapeof the shield may be varied to provide greater radiation of one portionof rubber than another portion, such as an adjoining portion. Anapplication of this would be when a material is moving under a shieldwith an irregular edge during treatment by irradiation. Also, the depthto which radiation will penetrate different areas of a shield may bevaried by making different portions of the shield of different shieldingmaterials.

By irradiating natural rubber or synthetics such as butadiene-styrene,polybutadiene, polyisoprene, etc., the molecular structure isrearranged. Other rubbers, perhaps known by other names, will becomecommercial and may be used as disclosed herein. The rearranged rubber ispartially or completely cured. By that it is meant that rubber which isthermoplastic when irradiated becomes partially or entirely thermoset(vulcanized) with or without sulfur.

Irradiation has no beneficial effect on so-called "butyl" (copolymer ofisobutene and either isoprene or butadiene) rubber and certain otherrubbers including butyl derivatives.

Radiation may be used to treat a green tire or part of a green tire, orthe tread in retreading, or a tread produced from ribbons of tread stockin retreading or the extruded tread stock in the manufacture of newtires or in retreading.

The rubber may be cured instantaneously by subjection to irradiation,and this may be done in a continuous operation in which the source ofradiation and the rubber are moved continuously relatively to oneanother. Alternatively, the rubber may be cured by progressiveirradiation. Progressive irradiation is accomplished by partially curinga piece of rubber in one exposure to the source of radiation, and thengiving it one or more additional exposures each of which partially curesthe rubber, until the rubber is cured. For example, by exposing the samerubber a number of times as by rotating a tire continuously and applyinga thin layer of the rubber to the tire as it is rotated, and continuingthe application of the thin layer throughout several rotations of thetire and as each thin layer is applied to the tire, exposing the rubberto irradiation to partially cure it so that as the tire is rotated anumber of times in building up a desired thickness of the carcass ortread and by continuing the rotation a number of times after completingthe application of the rubber, the rubber is progressively andcompletely cured.

The production of new tires will be discussed, and the retreading oftires; also equipment used in such manufacturing procedures.

FIG. 1 is a section through a green tire with a liner with the innersurface being irradiated;

FIG. 2 is a section through a mold containing a tire being cured withoutan air-bag or bladder;

FIG. 3 is a section through a conventional mold provided with means forextrusion of tread rubber into the mold; and

FIG. 4 is an elevation of a stand with a tire being retreaded on it,with the tread stock being extruded, and means for shaping the tread;

FIG. 5 is a section on the line 5--5 of FIG. 4 showing a roller that maybe used for shaping the tread stock in position on a section through atire being retreaded;

FIG. 6 is a section through a modified roller;

FIG. 7 is a section through a scan horn irradiating the entire centralportion of a tire tread stock with the edges of the tread stock coveredby shields;

FIG. 8 is a section through a scan horn irradiating only the shouldersof a tire tread stock;

FIG. 9 is a plan view of the tread stock and shields of FIG. 7;

FIG. 10 is a plan view of the tread stock and shields of FIG. 8;

FIGS. 11 and 12 are each a plan view of a tread stock moving under ashield;

FIG. 13 is a section through a green tire over which is a shield with anopening in it to provide radiation of a shoulder-to-shoulder portion ofa tread stock between the thin edges;

FIG. 14 is a section through a green tire over which is a shield withopenings in it to provide radiation of the shoulders of the tread stock;

FIG. 15 is a section through a tread stock with separate shieldscovering the thin edges;

FIG. 16 is a section through a tread stock with separate shieldscovering the thin edges and the central section to provide radiation ofportions of the green tread which will become shoulders of the finishedtread;

FIG. 17 is a section of the equipment shown in FIG. 11, on line 17--17,with a scan horn above the shield;

FIG. 18 is a section through a tread stock partially covered by thickerand thinner shields;

FIG. 19 is a section through a tread stock showing degree of cure afterone exposure; and

FIG. 20 is a section through the tread stock of FIG. 19 after beingsubsequently exposed to another treatment in the shoulder portions,only.

NEW TIRES

The inner surface of a green tire with a liner, whether the liner becured before incorporation in the tire or whether the inner surface ofthe liner be cured after the green tire is formed, is resistant to thepassage of steam or hot water. Therefore, this green tire can be curedin a mold without an air-bag or bladder. The mold may be of usualconstruction except that there is no provision for an air-bag, andmodification for support and/or formation of the beads may be desirable.

FIG. 1 is an illustration of equipment that may be used for curing theliner of a green tire in which an uncured liner has been incorporated onthe tire-building drum. The green tire 5, provided with the liner 6, isplaced over a roller 8 the shaft 9 of which will ordinarily bemechanically driven, although it may be operated by hand. The green tireis readily placed over the roller as indicated in FIG. 1. Although theinner surface of the tire, and primarily the liner, may be cured by anymeans, it is preferably cured by electron irradiation. A suitable device12 for effecting irradiation is moved into the position shown in FIG. 1to effect the irradiation with the irradiation device directed towardthe liner. Normally, a longitudinal section of 12, extending throughapproximately the entire width of the tire, will give off rays, and theentire inner surface of the tire will be irradiated by moving thatsurface under the longitudinal section by rotating the roller 8.Normally the irradiation will not be sufficient to cure any more thanthe inner surface of the liner to a depth of perhaps 1/16 inch.

FIG. 2 illustrates a mold for curing any of these tires, and it will benoted that no air-bag or bladder is utilized. The mold is constructed inany usual manner. It is shown as being formed of an upper part 15 andlower part 16 with two bead rings 17 fitted into the upper and lowerparts to contact the beads of the tire 5. The bead-sealing ring 18 maybe inserted in the same operation that the conventional bladder orair-bag is inserted.

The steam or hot water is led into the mold through the pipe 19 andprovides sufficient pressure within the tire to force it against themold to groove the tread and form any desired identification and indiciamarks desired on the tire surface.

A new method of applying a tread to a green carcass is illustrated inFIG. 3. The carcass 20 is built up in a conventional manner, with orwithout liner 21, on a tire-building machine and the carcass 20 isplaced in the mold shown in FIG. 3, which may be heated in theconventional manner, which comprises a lower part 22 and an upper part23 with two bead rings 24 fitted into the upper and lower parts tocontact the beads of the tire 20. The mold is conventional except forthe orifice 26 through which tread rubber is injected, being fed fromnozzle 27. A conventional air-bag or bladder may be used or the processusing neither of these and previously described may be used. Hot wateror steam under pressure is used to expand the green carcass against thesides of the mold. This pressure, before the tread is injected into themold, may be less than conventional curing pressures and only sufficientto press the green carcass into position against the sides of the mold.The tread stock is injected at temperatures at which it flows readilyunder pressure, such as temperatures of approximately 280° F. andhigher, through orifice 26 from nozzle 27.

The tread stock is usually introduced at or near the low point of theempty portion of the mold cavity outside of the carcass. It may beintroduced at several points. As it is introduced, the air is ventedthrough the air vents usually found in the tire mold, or separate ventmeans may be provided. When the tread has been injected the pressure inthe tire is raised to conventional levels and the carcass is completelycured. It is impractical to thus inject tread stock which contains theusual quantity of sulfur and accelerator or the like for curing becausethe temperature required for rendering the rubber sufficiently fluid forinjection is high enough to cure such stock. An exception is, whencoldfeed extruders are used, in which case cold stock is fed into themachine and is raised to high temperatures only for a small increment oftime before being extruded. According to this invention, the curingagent added to the tread rubber is only sufficient to partially cure thetread so that it may be removed from the mold after curing the carcass,without causing damage to the tread, such as blowing. The tire is thenremoved from the mold and the tread is cured by rearrangement of themolecules of the rubber in the tread stock, by irradiation or othermeans. An advantage of this method is the elimination of inventories ofuncured treads with inherent savings such as floor space, investment,labor, etc.

Alternatively, if irradiation which penetrates to a sufficient depth isused, the tread may be cured in the mold before the tire is removed.

When tires are cured by irradiation, even though no sulfur be employed,reinforcing agents, antioxidants, antiozonants, etc. may advantageouslybe added.

Rubber, the molecular structure of which has been rearranged by electronirradiation may take various forms as a sealant. It need not be rubberirradiated on only one surface. Both surfaces of a sheet may beirradiated without irradiation of the central portion of the sheet orthe rubber sheet may be irradiated throughout. A sheet of rubberirradiated on both surfaces, with or without the central portionirradiated, may serve as a sealant for a 3-ply laminate. Thus, threesheets of rubber, in contact with one another, may be subjected toirradiation to cause them to adhere to one another. Or the surfaces ofthe central sheet may be irradiated, and while they are still tacky bepressed between the other two sheets. Or one or several small pieces ofrubber, perhaps each the size of a quarter of a dollar and, for example,1/8 inch thick, may be positioned separate from one rubber, and perhapswidely separated from each other, between two sheets of rubber orbetween two pieces of any material the molecular structure of which isnot altered by irradiation, and the whole subjected to irradiation, forexample progressive irradiation, to cause them to adhere to one another.

As disclosed herein, by irradiation which rearranges the rubber,adhesion between the partially cured and cured plies is improved.Adhesive may be employed to insure adhesion.

In cases where the carcass is thin or where tires have a steel ply orplies which may or may not form a belt, it may not be desirable topre-cure or partially pre-cure any portion thereof. Steel conducts heatmore rapidly than most fibers and plies of steel therefore require adifferent curing time, and no pre-curing may be necessary. Then theremay be cases where it is desirable to cure or partially cure one or moreof the carcass plies, or portions of the carcass ply or plies and thetread stock, or portion thereof.

PRE-CURING THE TREAD STOCK

It has long been the desire of the tire industry to reduce the curingtime of tires in the curing presses; the object being to reduceinvestment in equipment and floor space and thereby make substantialsavings. A way to accomplish this is, before the tire is cured in apress to cure or partially cure elements of the tire, such as the treadstock or a tire ply, which require long curing time in the press. Someelements or sections of elements of a tire, such as portions of thetread stock that form the shoulders of the tread, may require longercuring time than other sections or portions. This is because thoseelements requiring longer curing time are located deep in the tire andfarther removed from the heating surface.

For example, if portions of an element such as the inner portion of themiddle section of the tread stock is partially cured to such a degreethat it is cured to approximately 40 percent of full cure before goinginto the tire press, the curing time of the element in the press wouldbe substantially reduced and therefore the curing time of the tire maybe reduced accordingly.

When the molecules of a rubber piece are rearranged by radiation, theextent or degree of the cure depends upon the amount of therearrangement of the molecules. This depends upon the number of radswhich act on the rubber. A further consideration is the depth ofpenetration by the electrons, etc. and this is determined by the voltageused in the treatment. Irradiation which rearranges the molecularstructure is of great importance in the methods and processes disclosedherein. Two important reasons are (1st) with said irradiation, the depthof cure of any specific area to be cured and the degree of cure may becontrolled satisfactory. However, with heat and sulfur curing this isvery difficult and not practical. (2nd) The energy cost of curing byirradiation has been estimated to be less than the energy cost of curingby heat and sulfur. Due to tread design the tread stock is often anelement which lends itself to the process of a portion or portions beingcured or partially cured before the tire is cured. This is sometimescalled pre-curing or partially pre-curing.

The processes for accomplishing these objectives are disclosed in thefollowing disclosure and particularly the use of said irradiation andthe shielding of said irradiation.

When rubber is cured or pre-cured by irradiation which changes themolecular structure, some of the physical properties are different froma similar piece of rubber cured with sulfur and heat. For example,rubber cured by said irradiation has a little less tensile strength butmore resistance to crack growth than rubber cured by heat and sulfur. Intests it has been observed that rubber partially cured by saidirradiation has slightly more tack than similar rubbers partially curedby heat and sulfur. The fact that rubber cured by said irradiation hasdifferent physical characteristics makes possible processes whichproduce satisfactory results that are not accomplished with the presentpractice which uses heat and sulfur curing. It is generally accepted inthe tire industry that satisfactory results cannot be obtained byputting a cured or partially cured tread on a green or cured tirecarcass. The results are not satisfactory because it has been found thatduring service the elements cured or partially cured with sulfur do nothave adequate adhesion to the elements they contact and there isseparation between said elements causing a defect. However, it has nowbeen found that satisfactory adhesion can be obtained by partiallycuring a tire ply by electron irradiation and partially curing a treadstock by electron irradiation, both having been compounded with sulfur,and then putting the two together under pressure and completing the curewith heat. Also, it has been found that prior to assembly of the treadstock with the carcass, by partially curing by electron irradiation, aportion of the underside of a tread stock compounded for curingconventionally and then curing the assembled tire with heat and sulfur,the curing time of the tires was reduced 25 percent, the time beingreduced from 16 minutes to 12 minutes. The finished tread on the tiredid not show any evidence of undercure. A number of tires were made tothe same specification which specified a 16-minute cure. They were madewithout pre-curing the treads as above described. These tires were cured12 minutes instead of the specification requirement of 16 minutes andall treads were undercured as indicated by porosity and small holes inthe inside of the tread near the carcass. Thus, with said irradiationprocess, the curing time of tires may be substantially reduced andconsiderable savings effected.

It may be desirable to pre-cure or partially pre-cure a portion of asection of the tread stock as by irradiation which rearranges themolecular structure of the rubber in the tread stock prior to assemblingthe tread with the carcass or at any other time prior to final curing ofthe tire. It may be desirable to pre-cure by such irradiation only asection or a portion of a section of tread stock or it may be desirablenot to pre-cure a portion such as the thin edges of tread stock, or acentral section of the tread stock and to pre-cure only a portion of asection of said tread stock. The desire to use any of many choices willdepend to a great extent on the design of the tire and the tread. Someof these options will be described later. The irradiation may be appliedto the inner surface of the tread stock or the outer surface which formsthe surface of the tread which contacts the road. Sometimes thepre-curing or partial pre-curing of the outer surface will be applied tothe tread stock after assembly with the carcass, but the outer surfacemay be pre-cured or partially pre-cured before assembly with thecarcass.

The effectiveness of a shield to block all treatment by irradiationwhich rearranges the molecular structure usually depends on the densityof the shielding material and its thickness. A shield which permits thepassage of irradiation which rearranges the molecular structure limitsthe depth of treatment or cure which depth usually depends on thedensity (i.e. the mass per unit volume) of the shield material and itsthickness. The denser the material, the greater its ability to blocksaid treatment. For example, lead has a greater density than aluminumand therefore is more effective in blocking said treatment. In anyspecific material the thicker it is, the greater its ability to blockthe irradiation. A shield of a thickness which permits the passage ofradiation will reduce the depth of treatment, but does not necessarilyreduce the degree of treatment or cure.

FIG. 7 is a section through tread stock and equipment which irradiatesthe entire central section 85 of a tire tread stock 81, and FIG. 9 is atop view thereof. The section 85 of the tread stock will form thesection of the tread which will contact the road. The tread stock hastapered edges with thin portions 83 and thick portions 84. The sections89 of the thick section 85 of the tread stock will form the shoulders ofthe finished tread. On the inner surface of the tread stock are shownshields 87 which prevent the tapered edges from being irradiated. Analternative arrangement uses shields 87', shown in phantom, instead ofshields 87; they do not contact the tread stock and may be used inprocesses such as are shown in FIGS. 11 and 12 in which the tread stockis moved under the shields. Alternatively, the shields may be movedwhile the tread stock is stationary. The scan horn is 80. The dottedarea 85' on the inner side of section 85 shows a portion of the treadstock being treated and cured or partially cured.

FIG. 8 is a section through tread stock and equipment which irradiatesthe inner surface of the shoulders 89 of tread stock 81 and a top viewis shown in FIG. 10. The tread stock 81 has tapered edges with the thinportions 83 and thicker portions 84 and the entire thicker centralsection 85. On the inner side of the tread stock are shown shields 87which prevent the entire tapered portions from being treated. Shield 88prevents the central portion 82 of section 85 from being irradiated.This leaves only the shoulder areas 89 to be treated. The cured orpartially cured portions are indicated by the dotted areas 89' at theinner surface of 89.

The shields 87 and 88 rest on the tread stock. The stock and shields maybe stationary. Alternatively, the stock and shields may move togetherunder the scan horn. The shields may be some sort of continuous devicesuch as cylinders which rotate as the tread stock moves under them, incontact with them. The tread stock is usually extruded or calendered asa continuous strip, and may pass directly from the forming mechanismunder the scan horn. The tread stock may move under the scan horn asindividual pieces. The shields may be attached to the horn or beseparately suspended. Generally, the horn remains in a fixed position,but this is not necessary.

Shields 88' and 87', shown in phantom in FIG. 8, are in positions wherethey do not contact the tread stock. These may be used in processes suchas shown in FIGS. 11 and 12, and also in processes such as suggested inthe previous paragraph.

FIG. 11 is a plan view of tire tread stock 121 passing under shield 127'and being irradiated in the area 150 between the vertical dash-dotlines. The direction of movement of said tread stock is indicated byarrows. The shield 127' is between the scan horn, not shown, and thetread stock 121. It does not touch the tread stock. In the area 150being irradiated, the shield 127' covers the tread stock edges 124, andthe portion 128' of the shield protects a part of the central section ofthe tread and provides for greater radiation of the shoulders 129 thanthis central section. Therefore, as the tread stock moves under theshield, the shoulders 129 of the tread stock will be exposed totreatment a longer period of time than the center section of the stock126'. Thus the shoulders 129 are being treated to a greater extent thanthe center section 126'. FIG. 17 is a cross section on the line 17--17of FIG. 11.

FIG. 12 is a plan view of a tire tread stock 131 passing under shield137' and being irradiated in the area 151. The direction of movement ofsaid tread stock is indicated by arrows. The shield 137' is between thescan horn, not shown, and the tread stock which the shield does nottouch. In the area 151 being irradiated the shield 137' protects thetapered edges 134 of the tread stock and therefore the central section135 is all that is treated. In such processes it is necessary toregister or properly align the tread stock 131 under the shield 137'.Such alignment may be effected by well-known means such as roller guides(or stationary guides), electronic guide means, etc.

FIGS. 11 and 12 are illustrative of apparatus and procedures for movingirradiation means and a sheet or other article relative to one another.The article may, for example, include other material than rubber, suchas a metal article covered by a rubber or any synthetic or othermaterial to be irradiated. The shield need not be of uniform thickness,but may vary in thickness to provide varied depths of irradiation of therubber or other material. As indicated, the forward edge of the shieldused need not be straight. However, it may be straight; it may be curvedin any manner or slanted at an angle of less than 90° to the movement.Also, the shield may be composed of different materials which providedifferent depths of irradiation. Usually the scan horn will remainstationary and the tread stock will pass under it with shielding placedon the stock or fixed in a permanent position under the scan horn.

FIG. 13 is the section of a green tire 106 with tread stock 101 appliedthereto with shoulder section 109 and tapered edges with thin portion103 and thicker portion 104. Shields 107 protect the tapered edges. Thetire or the horn, or both, are rotated to subject the portion of thetire under the opening 105 to treatment.

FIG. 14 is the section of a green tire 106 with tread stock 101 appliedthereto with shoulder sections 109 and tapered edges with thin portions103 and thicker portions 104. Shields 107 protect the tapered edges andshield 108 protects a middle portion of the tread stock. The tire or thehorn or both are rotated to subject only the shoulders 109 throughopenings 105' to irradiation.

FIG. 15 is a section through equipment which irradiates the entire outersurface of section 95 of tread stock 91 which surface, when cured, willcontact the road. The portion 95' is cured or partially cured while theedges covered by shields 97 are not cured.

The scan horn is 90. This process may be used in cases when it isdesirable to partially cure the entire section 95, said section beingvery thick. Irradiating from both inner and outer sides facilitates thisobjective.

FIG. 16 is a section through equipment irradiating the surface ofsection 99 of tire tread stock 91 which sections will form the shouldersof a tire tread. Sections 99 are a part of section 95 which forms thesurface of a tread which surface will contact the road. The portions 99'indicated by dots are being cured or partially cured. Shields 97 shieldthe tapered edges from treatment and shield 98 shields a center portionof 95. Thus, sections 99 are the only unshielded areas. The scan horn is90. This process may be used in any of the processes described in whichthe shields contact the tread stock; and by positioning the shields outof contact with the stock other processes may be utilized.

FIG. 18 is similar to FIG. 8 and differs only in that the shield 86 usedon the middle of section 85 is thinner than that shown in FIG. 8. Theshields 87 are thicker than shield 86 and completely block the treatmentof the tapered edges of the tread stock. Sections of the tread stock 81which are not shielded and are irradiated as indicated by 89' show thatthe curing or partial curing of section 89' is deeper than the curing orpartial curing at 86' which depth is controlled by the thickness ofshield 86.

Shield 86 may be made of material different from and have less densitythan that of shield 87 in which case it may be as thick or thicker than87, and yet may not be as effective a shield as 87.

FIG. 19 shows tread stock 81 which has been treated by shieldingarrangement shown in FIG. 7. The cured portion 120 is the dotted area.The shoulders are 89.

FIG. 20 shows tread stock 81 which was first treated as in FIG. 19 andthen treated using the shielding arrangement shown in FIG. 8 so thatonly the shoulder sections 89 were successively treated, and were curedto a greater degree than the central portion of the tread as indicatedby the greater number of dots in area 121 than in area 120.

In considering the effect on rubber of irradiation that rearranges themolecular structure, two factors are important, namely, (1) the depth ofpenetration of the irradiation and (2) the intensity or degree ofirradiation. We are here concerned with the effect shielding has onthese factors.

Shielding has heretofore been used as a preventative process because itabsorbs all radiation. However, as disclosed herein, it may be used tocontrol the depth of radiation and to control the degree of treatment orcure.

It may be desirable to treat an article with a greater degree oftreatment in one portion and a lesser degree of treatment in another.This may be accomplished by treating an article as shown in FIG. 8 andthen repeating the treatment after removing shield 88 so that bothsection 89' and section 82 have been treated, but 82 to a lesser degreethan 89'. This effect has been accomplished by treating section 89'twice and portion 82 only once.

This may also be accomplished by a process which involves passing atread or other article successively under two scan horns, the shieldingunder the first horn being arranged as shown in FIG. 8 using shields 87'and 88' and using shields under the second horn arranged as shown inFIG. 8 but eliminating shield 88'. Thus, by exposing the article underthe first scan horn with its shielding arrangement and then under thesecond scan horn with its shielding arrangement, the section 89' wouldbe treated twice and therefore to a greater degree than section 82. Thefirst and second horns may be set up in tandem and operated as acontinuous process wherein a conveyor or other device would convey thearticle, such as tread stock, exposed to the first scan horn and thenexposed to the second scan horn. Various combinations of the aboveapparatus may be used. Thus, when two sections or two portions of atread are subjected to irradiation which rearranges the molecularstructure, one section or one portion is cured to a greater degree thananother section or portion.

One section of an article may be treated to a greater depth thananother. A way of doing this is shown in FIG. 18 wherein section 89' istreated to the same degree but to a greater depth than section 86'. Thisis accomplished by the shieldings. Shields 87 block all treatment fromthe tapered edges 83 and shield 86 permits some treatment to passthrough it limiting the depth of the cure but not the degree of cure.Therefore the shoulders 89' are cured to a greater depth than theportion 86' which is indicated by the dotted areas. When using electronirradiation this may be accomplished without shielding, by varying thevoltage. The higher the voltage, the greater the depth of cure.Accordingly, a first section or portion may be treated by suchirradiation using a higher voltage than is used in a second section orportion. Thus the first section or portion will be cured to a greaterdepth than the second section or portion. This may be advantageous incases such as in the treating of tread stock where it may be desirableto treat the shoulder section of tread stock to a greater depth than amiddle portion.

Reference is made to FIGS. 7, 8, 9, 10, 13, 14, 15, 16, 17, 18, 19 and20 which refer to pre-curing or partially pre-curing tread stock. Otherproducts may be treated by the same processes to rearrange the molecularstructure.

The scan horn in the drawings scans the electron beams around a centralaxis and through a titanium alloy window so as to properly treat thematerial. Any suitable radiation device that rearranges the molecularstructure may be used.

The tread stock 81 of FIGS. 7, 8, 9, 10 and 18, 19 and 20, and treadstock 101 in FIGS. 13 and 14 and tread stock 91 of FIGS. 15 and 16 is ofthe usual shape, the outer edges being thinner than the central section,and tapering toward the outer edges. Unless these edges are shielded,precuring by radiation may cause over-curing when the tire issubsequently cured by a conventional or other method. In usual practiceshielding would be used to block all treatment or control the depth oftreatment. Generally, shielding will be used to prevent any pre-curingof the tread stock edges by irradiation. The section 85 in FIGS. 7, 8and 18 is that section of the tread stock which will form the section ofthe tread which will contact the road. The sections 89 of the treadstock will form the shoulders of the tread.

FIGS. 7 and 15 show shielding the outer edges of the tread stock toprevent curing. The tread stock may be extruded or calendered or formedby any other method and any method may form the tread stock in the shapeshown in FIGS. 7 and 8 or as a ribbon or a strip and said tread stockmay be treated by irradiation which rearranges the molecular structure.Said treatment may be effected before said tread stock is assembled withthe tire or anytime before the whole tire is subjected to final curing.The shields 87 of FIG. 7 may be thick aluminum sheets, e.g. 1/4 inch (or0.6 to 0.7 cm.) thick. They may be placed on the inner surface of treadstock as shown in FIGS. 7 and 8, or raised somewhat as shown in phantomin these figures.

FIG. 8 shows an additional shield 88 covering the central portion 82 ofsection 85 of the tread stock, which shield may completely absorb all ofthe irradiation and prevent curing under the shield.

The outer sections 89 of the thick central section 85 of the tread stockare not shielded in FIGS. 7 or 8. This may be desirable if in theultimate shape of the tread these outer sections 89 are shaped intoshoulders that are thicker than the rest of the central section of thetread. By this process desired portions of the shoulders may be precuredor partially pre-cured by irradiation which rearranges the molecularstructure to a greater degree than other portions of the tread stock.Such tread designs which include thick shoulders are common and thecuring of them has presented a problem which the industry has not yetsuccessfully overcome. The extra thickness of the tread shoulders hasnecessitated long curing times sufficient to cure the shoulders of thetread which time periods are, in most cases, much longer than needed tocure the rest of the tire. Thus, by pre-curing or partially pre-curingthe shoulder area of the tread stock or portions thereof by the saidirradiation, as herein disclosed, the curing time of the tire may beshortened and thus substantial saving may be effected.

By pre-curing portions of the shoulder sections and other portions ofthe tread by such irradiation, the final curing time of the tire may befurther reduced.

As indicated, the shields need not touch the tread stock. They may beplaced at an angle or they may extend in a straight line covering thethin edges of the tread stock. FIG. 13 shows shields 107 located in thelatter position. FIG. 19 shows such shields 107 and an additional shield108 over the central section of the tread stock.

It is usually advantageous to have the irradiation which rearranges themolecular structure directed against the underside of the tread stock,for in most cases it may be only necessary to pre-cure or partiallypre-cure the tread stock adjacent the inner surface. In the conventionaltire press approximately 80 percent of the heat to cure the treadsection of the tire comes from the inside of the tire and 20 percentfrom the mold which contacts the outside of the tire. Due to the factthat most tire fabrics are a poor conductor of heat and the tire treadis thick, the design of many tires is such that the most difficult partto cure is in the shoulder of the tread next to the carcass and in suchcases the first indication of undercure is in the shoulder area. It hasbeen found that by partially curing the tread stock with saidirradiation prior to assembly with the carcass of the tire, thetire-curing time can be reduced and the tire will be completely cured.This may be accomplished by partially curing by said irradiation atleast a portion adjacent the inner side of the tread stock. In somecases the said curing may be only in the shoulder section 89 (FIG. 8) ofthe tread stock. In another case the curing may only be in the section85 (FIG. 7) which forms that section of the tread which contacts theroad. The section or sections to be cured and the depth and degree ofcure by said irradiation will be determined to a great extent by thedesign of the tire.

In preparing a tread stock for a tire it may be desirable to pre-formthe tread stock before applying it to the carcass. The stiffness and/ornerve in the tread stock may make it difficult to apply to the carcass.After being applied, the increase in the nerve may make it difficult tosecure it in position against the carcass so as to be properly curedduring the curing operation. In this situation the nerve may besufficient to cause the tread to have a tendency to pull away from thecarcass. When a treated tread is changed in shape, the nerve in thetread stock tends to pull it back toward its original shape. In somecases it may be desirable to pre-form the tread stock prior to itsapplication to the carcass. The object of this is to kill the nerveeffect just described. This may be done cold or by warming the treadstock before pre-forming. However, when a tread stock is treated byirradiation which rearranges the molecular structure, it may bedesirable to pre-form it immediately following said operation while thetread stock is still warm, having been slightly heated during theirradiation. Such pre-forming may give the tread stock the general orapproximate shape it will have when applied to the carcass. In somecases it may be desirable to pre-form the tread stock before or whilebeing irradiated. These methods may be used with tread stock and otherarticles.

Thus the curing or partial curing of an article by such irradiation,shaping and then completing the cure in another operation may beadvantageous.

It is to be understood that methods and apparatus disclosed herein maybe used in the manufacture of new tires, retread tires and otherarticles.

RETREADING TIRES

Various ways are disclosed for retreading tires. In each case thecarcass will be prepared for retreading in the usual manner by removingunwanted tread and, depending upon the shape of the retread which is tobe applied, a part of the sidewall stock may be removed, all of which iscustomary in the different methods of retreading, using differentequipment.

FIG. 3 shows a mold for extruding tread stock into position on theuncured or cured carcass of a new tire. The equipment of FIG. 3 and thegeneral method there disclosed may be used for applying the tread stockto a carcass which is to be retreaded; this operation taking place afterthe carcass has been prepared in the usual manner. It may be desirableto use air at room temperature or cooler, and water at tap temperatureor cooler in the tire to create pressure in the tire. It may also bedesirable to so design the mold that the heating cavity is onlyapproximately over the tread stock which is being applied.

The advantages of this method of retreading tires are elimination oftread-building facilities and the inventories of prepared uncured treadsall of which reduce costs. Also the carcass is subjected to less heatwhich has a deteriorating effect.

Instead of extruding the tread stock into a mold, the tread stock may beextruded onto a prepared carcass by rotating the carcass and using asuitably shaped nozzle that covers the width of the tread, or a narrowernozzle, the stock being reciprocated back and forth over the surface ofthe carcass to build up a retread. Suitable apparatus is illustrated inFIG. 4. The extruded rubber will ordinarily be heated to approximately280° F. or lower or higher to make it sufficiently plastic to be used asdescribed. It may or may not contain sulfur and/or curing agents and/oraccelerators. Some volatile solvent may be added to the rubber whichwill be evaporated before the curing of the tread is commenced, althoughusually this will be avoided because of the danger of solvent vaporforming pockets in the tread.

The methods illustrated in FIGS. 4 and 5 are particularly designed forthe retreading of airplane and truck tires which have a tread which isonly grooved, but may be used for any tires. FIG. 4 shows stand 50 withaxle 51 supporting wheel 52 with rim 53 on which the tire carcass 54 ismounted. A valve 56 in the rim through which the tire may be inflatedgives it some rigidity during the application of the tread stock. Thetire is provided with a scuff ring 57, but it is to be understood thattires of any shape and design may be retreaded by the method disclosed.As illustrated in FIG. 4, tread stock 58, sufficient to form the tread,is extruded from extruder 60 through nozzle 61. A forming tool 65 ispositioned on the supporting means 66 to shape the tread as the treadstock is extruded; and, if desired, forming tool 65 may exert somepressure to force the formed tread against the carcass. There may beadditional forming tools, such as 65, at other points on thecircumference of the tread for the purpose of shaping and/or pressure.The scan horn 59 may be located to treat the tread stock at any desiredstage of its formation. For example, it may be located to treat thetread stock immediately after it leaves the nozzle 61, or the scan horn80 of FIGS. 7 and 17 may be directed to treat the underside of the treadstock as it passes on a conveyor (not shown) past the horn. After thetread stock is applied to the carcass, the tire may be rotated severaltimes for the purpose of shaping and/or pressure.

The tread stock may be extruded with the proper tread outline andtread-forming tool 65 may be positioned on the supporting means 66 tomaintain the proper shape and/or exert pressure on the tread to press itagainst the carcass. There may be other forming tools, such as 65, atother points on the circumference of the tire.

Various methods of shielding and pre-curing have been discussed. Whereapplicable, tread stock to be used in retreading may be treated as theredescribed.

Another method of operating is to extrude the tread stock as a thinribbon the width of the tread, while the tire is being rotated, andafter quite a few rotations sufficient tread will be applied to build upthe desired tread thickness. As the ribbons are being applied to thetire, the tread-forming roller will shape them to the proper design. Aroller 70, such as illustrated in FIG. 6, may be used. The carcass 67 isshown with green tread 68 built upon it.

Another method of operating is to extrude a tread stock as a thin,narrow strip while the tire is being rotated. The strip is oscillatedback and forth across the tread portion and after quite a few rotationssufficient tread will be applied to build up the desired treadthickness. As the ribbon is being applied to the tire the tread-formingtool 65 or tools shape it to the proper design. A tire retreaded inmanners just disclosed, is preferably cured by electron irradiationwhich may be accomplished by rotating tire and wheel 54 and 52,respectively, under a radiation device such as device 12 shown in FIG.1; and, if desired, may be cured in a conventional manner or acombination of both. A grooved tread design may be cut into the tread byany conventional method or a groove may be rolled into the green treadby forming tool as shown in FIG. 6, preferably after the green tread hasbeen built up or while the last layer is being laid on the green tread.

A method which is preferred is illustrated by FIG. 4. Tread stock 58,being a thin ribbon, for example, approximately 1/8 inch thick, andapproximately the width of the tread, is extruded as the tire is rotatedand the tread is built up to any desired thickness. Forming tool 65shapes the tread and several other forming tools may be used. Radiationdevice or horn 59, similar to or identical with device 12 in FIG. 1, isillustrated in FIG. 4. It only partially cures the green tread duringeach exposure as the green tread is passed by it. The cure may, forexample, be only a one-fourth cure. The radiation device may be adjustedto cure to a depth of 1/2 inch, more or less. At the completion of eachrotation the surface is only partially cured and, therefore, the nextlayer of hot stock adheres to it. The green tread is progressivelyvulcanized as the rotation continues and the successive layers areadhered to one another.

If a layer of the green tread is one-quarter cured on each exposure, atthe completion of the fourth rotation the first layer is fully cured,the second layer is three-fourths cured, the third layer is one-halfcured, and the fourth layer is only one-fourth cured. This "progressiveirradiation" continues until the last layer is applied and then the tireis given three additional rotations which cures the last three layers.

A ribbon not the full width of the tread may be used and oscillated backand forth across the tread surface until the desired tread thickness isobtained, the level of radiation being adjusted to obtain the propercure.

Grooves in the tread may be made by the use of a forming tool such asthe tool 70 shown in FIG. 6.

In preparing a multi-layer tread stock, one layer or a part thereof maybe treated with irradiation which rearranges the molecular structurebefore said layer is placed in contact with another layer which may ormay not have been treated with said irradiation. This may be done beforethe layers are applied to the carcass or during said application.

In each of the retreading operations in which the tread stock is curedby irradiation, this tread stock may include sulfur and other curingingredients, or it may contain no such curing compositions becauseirradiation rearranges the molecular structure of the rubber and thuscures it. A small amount of sulfur may be included in such tread stock,and the extrusion will take place rapidly before the rubber becomesobjectionably cured at the extrusion temperature. The amount of curingingredients that can be incorporated in the tread stock will depend uponthe extruding temperature and the length of time that the tread stock ismaintained at this temperature. It is desirable to include a smallamount of sulfur and accelerator so that the tread stock will cure to aslight extent after it has left the extrusion device and been shaped onthe carcass. Such setting of the retreading stock will facilitatehandling the retreaded tire before the cure is completed. If a normalamount of sulfur, etc. are included in the rubber, unless the timeduring which the stock is heated is very short, curing will set in andthe rubber will become pre-cured before it is shaped on the carcass. Anexception is, when cold-feed extruders are used, in which case coldstock is fed into the machine and is raised to high temperatures onlyfor a small increment of time before being extruded.

The advantages of these methods of retreading include not heating thecarcass in a mold, and, therefore, the life of the tire is increased andthe tire may be retreaded a greater number of times, the curing time isshorter, press equipment is eliminated and inventories of green treadstocks are eliminated and thus savings in cost are made.

Various methods of treating tread stock for retreading which aredisclosed herein may be utilized in the treatment of tread stock for newtires.

Apparatus and processes for forming treads for retreading and new tiresand curing the tread stocks by electron irradiation have been disclosed.These tread stocks may be of ordinary rubbers (except those which cannotbe cured by electron irradiation, such as butyl rubber), and it has beenexplained that no sulfur is required for curing by irradiation. Adesirable tread stock material is a high molecular weightbutadiene-styrene copolymer such as has been found desirable for treadstocks, but which is of high viscosity and difficult to hand in ordinaryprocessing equipment. Reinforcing agents, antioxidants, antiozonants,etc. may be included even though no sulfur is added.

Shielding of less than the whole of any such body of material preventsor controls the effect of the irradiation. Shielding may be utilized toprevent such irradiation from contacting one or more portions of anobject or composition, etc. and producing a chemical or other effectthereon, and to control the extent or depth of irradiation on an objector composition. By using two or more shields, the same or differenteffects may be produced in different volumes of a material beingtreated, such as the depth and/or intensity of the effect of theradiation. Shields of different compositions may be used simultaneouslyor successively, and a single shield may comprise different areas whichhave different effects on irradiation. Thus the foregoing disclosure isillustrative of the equipment which may be used and the effect ofshielding on different materials for different purposes.

In the following claims, the designations below are used in thefollowing specific meanings, which are in common use in tire factories:

When a rubber composition containing all of the prescribed ingredientsis extruded or otherwise shaped, in profiled strip form for applicationto a tire, it is referred to as "tread stock".

When the tread stock has been applied to a tire carcass, it is called"green tread".

When the tread stock has been sufficiently cured for service on a tire,it is called "tread".

I claim:
 1. The process of preparing a tire tread stock which includesrubber which is curable by electron irradiation, which process comprisestreating and thereby at least partially curing at least a portion ofsaid tire tread stock by exposure to electron irradiation or other meansof radiation having the same curing effect on the exposed rubber, beforethe at least partially uncured tire with said treated tread stockassembled thereon is placed in a mold for the final cure of the tire. 2.The process of claim 1 in which the irradiation is effected byelectrons.
 3. The process of claim 2 in which the tread stock isirradiated with said irradiation from one surface such that beyond thedepth at which said rubber is irradiated there is uncured rubber, andthereafter curing said uncured rubber.
 4. The process of claim 2 inwhich the inner side of the tread stock is partially cured by saidirradiation prior to curing the outer surface of the tread stock.
 5. Theprocess of claim 2 which comprises partially curing at least a portionof the tread stock by irradiation and thereafter subjecting at least apart of said portion of the tread stock to further curing.
 6. Theprocess of claim 2 in which a first surface of the tire tread stock isat least partially cured by electron irradiation using such voltage thatsaid surface is cured to a greater degree than the opposite surface. 7.The process of claim 2 in which a surface of extruded tread stock isirradiated and the irradiated surface and a carcass surface arethereafter brought into contact.
 8. The process of claim 2 in whichrelative movement is effected between said irradiation-curable rubberand the source of the irradiation and the irradiation enters only onesurface of the rubber throughout the movement.
 9. The process of claim 1in which multi-layer stock is to be incorporated in a tread, and inwhich at least a portion of one layer of said stock is at leastpartially cured by said irradiation.
 10. The process of claim 9 in whichthe irradiation is effected by electrons.
 11. The process of claim 10 inwhich, after said curing, said layer which contains rubber which iscurable by said irradiation is placed in contact with another layer. 12.The process of claim 10 in which said layer which contains rubber whichis curable by said irradiation will be the inner layer of said tread andsaid inner layer is placed in contact with a tire carcass.
 13. Theprocess of claim 10 in which said layer which contains rubber which iscurable by said irradiation and is partially cured by said irradiationwill be the outer layer of said tread.
 14. The process of claim 1, whichprocess comprises curing or partially curing at least an inner portionof said tread stock by exposure to said irradiation.
 15. The process ofclaim 14 in which the curing is effected by exposure to electronirradiation.
 16. The process of claim 1 which comprises curing orpartially curing at least an outer portion of said tread stock byexposure to said irradiation.
 17. The process of claim 16 wherein thecuring or partial curing is effected by exposure to electron radiation.18. The process of claim 1 in which both surfaces of the tread stockinclude rubber which is curable by said irradiation, which processcomprises treating from both surfaces by exposure to said irradiation.19. The process of claim 18 wherein the curing is effected by exposureto electron irradiation.
 20. The process of claim 1 wherein said portionwill contact the carcass.
 21. The process of claim 20 wherein the curingis effected by exposure to electron irradiation.
 22. The process ofpreparing a tire tread the tread stock for which includes rubber whichis curable by electron irradiation and curable by sulfur and heat whichprocess comprises at least partially curing at least a portion of saidtread stock by exposure to electron irradiation or other means ofradiation having the same curing effect on the exposed rubber andthereafter assembling said tire tread with other tire elements andcuring said portion by sulfur and heat.
 23. The process of claim 22wherein the irradiation is effected by electrons.
 24. The process ofpreparing a tire which comprises winding onto a carcass a length oftread stock which is treated with electron radiation or other means ofradiation having the same curing effect on the exposed rubber, and byrelative rotation between the tread and a source of such treatment,progressively curing the tread as it is wound onto the carcass and thesuccessive layers are adhered to one another, and continuing theprogressive curing by such treatment until the last layer of the treadis wound onto the carcass and cured.
 25. The process of claim 24 inwhich the irradiation is effected by electrons.
 26. An unfinished tirehaving a green tread at least a portion of the thickness of which iscurable by electron irradiation or other means of radiation having thesame curing effect on the exposed rubber, at least a portion of thethickness of which green tread has been only partially cured by exposureto such irradiation and contains sufficient chemical curing ingredientsfor completion of cure.
 27. A green tread as in claim 26 in which thepartial cure was effected by exposure to electrons.
 28. A pneumatic tirethe tread of which is not completely cured, a portion of the thicknessof the tread adjacent the carcass comprising rubber curable by electronirradiation and which portion is at least partially cured by exposure tosaid irradiation, at least most of the exposed surface of the treadbeing uncured or cured to a lesser extent than said portion adjacent thecarcass.
 29. A green tire no part of which is completely cured, and themajor parts of which contain an unreacted curing agent, and at least aportion of the tread of which has been partially cured by exposure toelectron irradiation or other means of radiation having the same curingeffect on the exposed rubber.
 30. A tire of claim 29 the outer surfaceof the tread of which is partially cured by exposure to electronirradiation or other means of radiation having the same curing effect onthe exposed rubber.
 31. A tire of claim 29 the inner surface of thetread of which is partially cured by exposure to electron irradiation orother means of radiation having the same curing effect on the exposedrubber.
 32. A tire of claim 29 with at least a portion of one surface ofits tread cured to a greater degree by exposure to electron irradiationor other means of radiation having the same curing effect on the exposedrubber than the opposite surface.
 33. A tire of claim 29 wherein theradiation was electron radiation.
 34. A tire of claim 30 wherein theradiation was electron radiation.
 35. A tire of claim 31 wherein theradiation was electron radiation.
 36. A tire of claim 32 wherein theradiation was electron radiation.
 37. A tire of claim 33, both surfacesof the tread of which have been subjected to electron radiationtreatment.
 38. A tire of claim 33 having a multi-layer tread at leastone layer of which has been subjected to electron radiation treatment.39. The process of preparing a tread for a pneumatic tire which includesrubber containing sulfur which rubber is curable by exposure to electronirradiation or other means of radiation having the same curing effect onthe exposed rubber, which process comprises effecting the curing of saidtread by a combination of curing processes, first partially curing atleast a portion of said rubber by exposure to electron irradiation orother means of radiation having the same curing effect on the exposedrubber and thereafter curing said rubber with heat and sulfur.
 40. Theprocess of claim 39 in which said tread includes rubber curable byelectron irradiation and rubber curable with heat and sulfur, whichprocess comprises first partially curing by exposure to electronirradiation and thereafter curing with heat and sulfur.
 41. The processof claim 39 which process comprises first partially curing by exposureto electron irradiation and thereafter curing by another method.
 42. Theprocess of preparing a molded tread for a tire which tread includesrubber curable by exposure to electron irradiation or other means ofradiation having the same curing effect on the exposed rubber, whichprocess comprises after said rubber has been incorporated in a treadstock treating and thereby partially curing at least a portion of saidrubber by exposure to said irradiation and thereafter placing said treadstock in a mold.
 43. The process of claim 42 wherein said tread includesrubber curable by electron irradiation, which process comprisespartially curing at least a portion of said rubber by exposure toelectron irradiation before placing said tread stock in a mold.
 44. Theprocess of preparing a tread for a tire which tread includes rubbercurable by exposure to electron irradiation or other means of radiationhaving the same curing effect on the exposed rubber, which processcomprises after said rubber has been incorporated in the tread stockpartially curing said rubber by exposure to said irradiation andthereafter curing the tread in a mold.
 45. The process of claim 44wherein said tread includes rubber curable by electron irradiation andpartially curing said rubber by exposure to electron irradiation andthereafter curing said tread in a mold.
 46. The process of preparing atread for a tire the green tread for which includes rubber which iscurable by electron irradiation which process comprises at leastpartially curing at least a portion of said green tread on the carcassby exposure to electron irradiation or other means of radiation havingthe same curing effect on the exposed rubber before molding of theassembled thread.
 47. A tire having a green tread made by the process ofclaim 46 in which the portion at least partially cured includes theinner surface and the radiation was electron irradiation.
 48. Theprocess of claim 46 wherein the radiation is electron radiation.
 49. Theprocess of preparing a tread for a tire the green tread for whichincludes rubber which is curable by electron irradiation and curable bysulfur and heat which process comprises at least partially curing atleast a portion of said green tread by exposure to electron irradiationor other means of radiation having the same curing effect on the exposedrubber and thereafter curing said green tread rubber by sulfur and heat.50. The process of claim 49 wherein the radiation is electron radiation.